Serial ATA (SATA) is a storage interface standard (Serial ATA Specification, Revision 2.6, published February 2007) developed in 2003 to replace the aging Parallel ATA (PATA) standard. Serial ATA offers a number of advantages over Parallel ATA such as a faster data transfer rate due to differential signaling. SATA controllers may also include a standard interface known as the Advanced Host Controller Interface (AHCI). AHCI (AHCI Revision 1.2, ratified April 2007) enables several advanced features such as hot swapping and Native Command Queuing. In 2004 the SATA interface was expanded to include external SATA (eSATA) to allow SATA devices to be deployed in external enclosures with minimal modification (the eSATA specification is included in the Serial ATA Specification, Revision 2.6).
The SATA interface defines the connection between a SATA host adapter and a SATA device adapter. A host may be for example a computer, a laptop, a server, or a device that can connect to a storage medium. A device may be a hard disk drive, a memory, a DVD drive, a CD drive, or any device, co-located with the host or not, that utilizes a storage medium. The SATA adapter includes an Analog Front End (AFE) which acts as an interface between the SATA adapter's processor and the physical medium. The AFE converts analog differential data signals received over the physical medium to digital data signals which it transmits to the adapter's processor. The AFE also converts digital data signals received from the adapter's processor to analog differential data signals which it transmits over the physical medium.
FIG. 1 shows a typical connection between a SATA host AFE 100 and a SATA device AFE 110. The SATA interface connection includes digital data signals TX data and RX data and analog differential data signals TX+/TX− and RX+/RX−. The SATA interface connection also includes signals ComWake, ComInit, and ComReset which are Out Of Band (OOB) signals. OOB signals are transmitted over the same signal lines as data, but have unique characteristics that differentiate them from normal data signals and allow the SATA interface to distinguish between OOB signals and normal data signals. The AFE may include a squelch circuit, an Out Of Band signal detector circuit, or other circuitry to distinguish between data signals and OOB signals.
According to the SATA specification, OOB signals are used in three instances: to initialize communication with a host, to bring a device or host out of a power-down mode or to force a hard reset in a device. When compared to normal data signals, OOB signals are used very infrequently. Despite this fact, the SATA and AHCI specifications require that the squelch circuit and OOB detector circuit are constantly powered and activated. In fact, no current apparatus or method exists to allow the power down and deactivation of these circuits while maintaining proper SATA host and device operation.